Solution Summary: Hand-held Grinders with Wet Dust Suppression

A hand-held grinder with wet dust suppression delivers water to the surface to reduce airborne contaminants while smoothing masonry surfaces.

Description:

Hand-held surface grinders are often used to smooth poured concrete surfaces after the forms have been removed. Hand-held grinders are also used to smooth granite, marble and other natural stone. Grinding concrete and natural stone generates a large amount of dust which is likely to contain high levels of crystalline silica and creates a hazard for everyone in the vicinity. Increasingly, nano-enabled masonry products are being used in construction that can also expose workers to inhaling engineered nanomaterials when the products are being cut or ground. Concrete roofing tiles that contain nano-size titanium dioxide are an example.

Using water to suppress the dust may be easier than using local exhaust ventilation in some circumstances, and is an important dust control option to consider. These engineering controls use a pump or line pressure to deliver water to the grinding surface where it combines with particles and reduces airborne dust levels.

If properly designed and used, exposures can be significantly reduced. If use of grinders is brief and intermittent, this may reduce exposures enough that a respiratory protection program isn’t required. Continuous use may exceed the OSHA Permissible Exposure Limit, even with the use of wet dust suppression, however.

Intertool DS 175 7-inch planetary polisher with wet dust suppression

Used to grind, hone, polisher or clean steps, counter tops, floor edges, under toe kicks or other small areas

Used for grinding and polishing gemstones, rock materials, marble and granite

Cost: $375 (verified 2/2011)

Power requirements: 120 volts, 7.9 amps

Polishing disc diameter: 3, 4 or 5 inches

Blade speed: 2,000 to 4,000 RPM

Weight: 6 pounds

Sound pressure level: Not available but likely to exceed 90 dBA (OSHA’s Permissible Exposure Limit for an 8-hour time-weighted average)

Risks Addressed:

Grinding concrete, stone and masonry materials containing crystalline silica is a high dust activity that in the absence of controls would place workers at risk of lung disease, cancer, chronic obstructive pulmonary disease (COPD), lung scarring and silicosis with prolonged exposure. Silicosis is an incurable, sometimes fatal disease. Such disease is well documented in the Vermont granite quarries and stone cutting sheds, and in construction operations. The NIOSH-recommended exposure limit (REL) is 0.05 mg/m3 as a time-weighted average concentration for up to a 10-hour workday during a 40-hour workweek. OSHA has a new construction permissible exposure limit (PEL) for respirable crystalline silica of 0.05 mg/m3 as an 8-hour time weighted average (TWA).

Another less understood, but emerging hazard is engineered nanomaterials. Incredibly small particles are being added to a broad range of construction products to improve performance, but animal toxicity tests indicate a need for closer scrutiny. There is no evidence yet that engineered nanomaterials have caused harm in exposed workers. However, it is most important that exposures be limited and that precautionary approaches be used to reduce exposure and protect construction workers from the potential hazards of engineered nanomaterials. Nano-size ultrafine titanium dioxide, which can be present in nano-enabled masonry products, has been found to cause inflammation of the lungs and lung cancer in lab animals. The National Institute for Occupational Safety and Health (NIOSH) has determined that ultrafine titanium dioxide should be considered a potential occupational carcinogen. Other engineered nanomaterials that may be present in products used in masonry work could also potentially cause harm when inhaled by construction workers. Cutting nano-enabled concrete roofing tiles without engineering controls can generate excessive amounts of airborne dust that if inhaled by workers could increase the risk of developing respiratory disease (West GH, et al. 2016). It is likely that grinding nano-enabled masonry products will generate high levels of airborne dust and possibly engineered nanomaterials in the absence of any control measures designed to reduce exposures.

OSHA has no specific regulation or Permissible Exposure Limit (PEL) for any engineered nanomaterial. However, NIOSH has a recommended exposure limit (REL) for ultrafine titanium dioxide of 0.3 mg/m3 as a time-weighted average (TWA) concentration for up to 10 hours/day during a 40-hour week. The intent of the REL is to lower the risk to workers of the potential for developing lung cancer.

How Risks are Reduced:

Water is delivered to the grinding disc where it combines with particles created by grinding of stone, concrete and masonry materials and the now larger particles settle. Silica in the concrete and masonry materials is only hazardous if it is inhaled and is not hazardous for skin contact. As long as the dust does not become airborne, the hazard is reduced. The extent to which these tools are effective in meeting recommended exposure limits has not been evaluated. For nano-enabled masonry products, wet dust suppression is also likely to be effective in reducing concentrations of airborne engineered nanomaterials in a worker’s breathing zone.

Using water will visibly suppress dust, but the extent that it reduces the small, respirable particles is unclear, without additional testing. Although exposure is not reduced to zero, substantial reduction is expected. This is dependent on the amount of water used, how effectively it prevents suspension of particles in the air, rotational speed of the grinder and the extent to which workers are exposed to resuspended dust after it dries. While there is no published sampling data on these specific tools, evidence indicates exposure to respirable silica can be significantly reduced through the use of wet methods.

In a survey of silica exposure during fabrication of granite countertops, Simcox et al. observed an average silica concentration of less than 0.07 milligrams per cubic meter during the use of water-fed grinders. They concluded “wet processes significantly reduced worker exposure to respirable crystalline silica and, in all cases, to below the state of Washington’s PEL of 0.1 mg/m3.”

In a study of granite processing facilities, Wickman and Middendorf stated that “the workplace controls, which are typically wet methods, implemented in the granite industry have been generally effective in reducing employees' exposures to below the OSHA PEL.” They recommended that “use of these controls should be implemented and enforced in other workplaces, such as rock drilling and abrasive cutting of concrete, where silica exposures remain problematic.”

There are no reported studies specifically evaluating the effectiveness of wet dust suppression methods in controlling construction worker exposure to engineered nanomaterials in masonry products when using grinders. However, because wet dust suppression methods with water-fed grinders has been demonstrated to significantly reduce worker exposure to silica, it is likely that wet dust suppression will reduce worker exposure to engineered nanomaterials when used for grinding on nano-enabled masonry products.

Effects on Productivity:

Wet dust suppression systems can have either positive or negative effects on productivity, but definitely improve the quality of the work by suppressing large amounts of airborne dust, which allows a cleaner, more efficient means of grinding.

Dust suppression also reduces site cleanup times. Dust suppression avoids exposing other workers, members of the public, adjacent property, cars and building occupants, which can increase liability and time-consuming disputes. Improved worker comfort is a result of reduced airborne dust which may in turn result in less fatigue for the worker and greater productivity. In some cases, particularly where grinder use is intermittent, wet dust suppression may be adequate to reduce the need to wear a respirator, and the need for an employer respiratory protection program.

Some additional issues should be considered. Time may be required to allow concrete and masonry materials to dry after grinding and before subsequent work, which will depend on the material, the amount of water used and the application. The grinder needs to be located near a water tank or another source of water.

Additional Considerations:

Grinding of concrete or masonry performed in the state of California must employ engineering controls, either wet methods or local exhaust ventilation, unless the employer can show that exposures are below the permissible exposure limit (subchapter 4, article 4, section 1530.1). New Jersey has a similar prohibition of dry cutting or grinding of masonry (Chapter 172).

The use of water controls may result in wet and slippery ground and walking surfaces. During cold weather this may lead to the formation of ice and an increased risk of slips, trips and falls. Grinding debris that is not removed from the work area while wet may become airborne once dried, posing an inhalation hazard to anyone in the area. Maintaining a work area free of debris and excess water reduces the risk of these hazards.

The use of water as a dust control increases the risk of shock when electricity is used in the same area. Electrical cords and extensions must be rated for the tool's power requirements, be regularly inspected, replaced when damaged, and used in combination with ground fault interrupt circuits.

The use of gasoline and diesel-powered generators, compressors, pumps and other equipment poses the risk of carbon monoxide exposure, particularly in areas where airflow is reduced. Steps to control exposure are important because the gas is invisible, odorless and tasteless. Poisoning by carbon monoxide can occur quickly indoors, but working outdoors does not ensure operators won’t be overcome. Small, inexpensive personal monitors should be worn by the operator to warn of unacceptable exposures.

Hand-held grinders frequently generate sound levels that are greater than 90 decibels, the OSHA Permissible Exposure Limit (PEL), and hazardous. Hearing protection should be worn when using grinders unless an industrial hygienist has conducted noise monitoring and indicated that hearing protection is not required.

As is the case with any construction equipment, users should follow manufacturer safety recommendations and comply with any applicable local, state or federal regulations.

Personal Protective Equipment

Work practice

Return on Investment

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